1. Field of the Invention
The present invention relates to a wavelength division multiplexing apparatus (WDM transmission apparatus) that multiplexes and divides plural signals in wavelength and then transmits the divided signals to thereby attain high-capacity transmission.
2. Description of the Related Art
As shown in FIG. 1, the WDM transmission apparatus includes a transponder unit that converts plural different signals into a specific wavelength, and a WDM unit (wavelength division multiplexing unit) that conducts wavelength multiplexing/division on the converted signal and optically amplifies the wavelength-multiplexed signal.
A wavelength that is subjected to wavelength multiplexing/division in the WDM unit is regulated by ITU-T G.694. The WDM unit generally multiplexes wavelengths that conform to wavelength grids which are regulated by ITU-T G.694. The WDM transmission apparatus of a high-capacity conducts wavelength multiplexing of 40 waves, 80 waves, or more. The transponder unit requires transponders as many as the multiplexed wavelengths. Accordingly, the more the number of multiplexed wavelengths increases, the more the scale of the WDM transmission apparatus is enlarged.
Upon starting (startup of) the WDM transmission apparatus, the transponders as many as the multiplexed wavelengths are connected to the WDM unit through optical fibers, respectively. At this time, wavelengths each corresponding to each wavelength received from a destination of the WDM selection need to be set to the transponders. In the existing circumstances, the connecting work is all conducted manually. The wavelengths of the transponders are also manually set by operator through, for example, a remote control from a central control station. Accordingly, in the start-up operation of the high-capacity WDM transmission apparatus, setting work related to a large number of wavelengths is required. Therefore, the wavelength setting work is very complicated, which leads to a high possibility of a setting error.
Also, in additionally providing (adding) a new wavelength for the WDM transmission apparatus that has already started the operation, the connection and setting work related to the new wavelength are required. In this case, the operator must give consideration to the wavelengths that have already been used to select unused wavelengths or to set the wavelength. In this situation, the operator must conduct the operation while checking a large number of items, which lead to a possibility of a setting error.
In order to eliminate the complication of the above-mentioned wavelength setting work, there has been already proposed a method of automatically setting the transmission wavelengths to the transponders. For example, Patent document 1 discloses “a wavelength-multiplexed light transmission system and an optical signal transmission control method”. In the technique disclosed in Patent document 1, in consideration of the fact that a wavelength multiplexing portion of the WDM unit has a filter and allows a light of only a specific wavelength band to pass therethrough, photodetectors for detection of light intensity are disposed in front and back of the filter to sweep the transmission wavelengths of the transponders in sequence. With this structure, the light intensity can be detected when a wavelength that coincides with that of the destination is set to the transmission wavelength. In addition, a control unit in the WDM unit notifies a control unit in the transponder unit of light detection information to determine the transmission wavelength of the transponders as a set wavelength. In the technique disclosed in Patent document 1, there is required a structure in which information is transferred between the control unit in the WDM unit and the control unit in the transponder unit. Therefore, in a case where the WDM transmission device is structured by the WDM unit and the transponder unit which are different in vender, there is a fear that it is difficult to control the transfer between the WDM unit and the transponder unit. Also, in the technique disclosed in Patent document 1, the transmission wavelength of the transponder is swept to determine the set wavelength. Therefore, a long period of time may be required for the determination.
Also, Patent document 2 discloses “a wavelength-division multiplex system and a method of automatically setting conversion wavelengths in the system”. The technique disclosed in Patent document 2 has not only a function of automatically setting the wavelength but also a function of preventing the misconnection of an optical fiber. The technique disclosed in Patent document 2 has a function of adding the wavelength information of itself by modulation of a main signal between the WDM unit and the transponder unit, with which the level monitor of a light that has passed through a specific filter of the WDM unit, and the demodulation and detection of the wavelength information which has been modulated after passing of the light are executed. As a result, it is possible to determine whether or not the wavelength to be set is accurately connected. The technique disclosed in Patent document 2 is required to provide each the transponder unit and the WDM unit with a modulation function for adding the wavelength information to the main signal.
As described above, in the techniques disclosed in Patent documents 1 and 2, both of the WDM unit and the transponder unit are improved (the function of automatically setting the wavelength is added) to realize the automatic wavelength setting.
[Patent document 1] JP 2004-274113 A
[Patent document 2] JP 2004-015328 A